1. Field of the Invention
The present invention relates to a power supply. More particularly, the present invention relates to a power supply for supplying power to a lamp with functions of dimming, over-current protection, over-voltage protection, arcing protection, and low-temperature start-up.
2. Descriptions of the Related Art
Nowadays, lighting has become indispensable to people's life, and commonly using for lighting are still lamps. Generally, in order to drive a lamp to emit light, an alternating current (AC) power supply is required. A frequency of the AC power supply shall match the impedance characteristics of the lamp, i.e., be maintained in a range from 40 KHz to 80 KHz, for driving the lamp. Besides the range, either an excessively high or an excessively low frequency of the AC power supply would result in increased impedance, i.e. a decreased gain, of the lamp.
In order to match up requirements in different surroundings, the power supply of a lamp may also be designed to provide the lamp with adjustable output brightness, i.e., a dimming function. Since the power supply of a lamp typically adopts a pulse width modulation (PWM) design, the dimming function may be accomplished by adjusting a duty cycle of the power supply, or by increasing a frequency of the power supply output to reduce the gain of the lamp.
However, when dimming a lamp with the above methods, there is still energy outputting to the lamp. Since the service life of the lamp is positively related to the illumination duration of the lamp, and the purpose of dimming the lamp is to decrease the output brightness of the lamp, the energy output continued during the dimming process may not only unnecessarily consume electric power, but also shorten service life of the lamp.
Also, the power supply may suffer surge current when open-circuited status, short-circuited status, or arcing status occurs. If the power supply cannot turns off timely when the aforementioned statuses occur, the lamp or the power supply may be damaged by the surge current.
Almost every kind of electrical products has a certain number of electronic elements interconnected via circuits. If there are any defects in the interconnections, for example, two adjacent bare electrical wires, arcing would occur therebetween. The arc is essentially a high-frequency current, which may damage the electronic elements of an electrical product and may further lead to the complete failure of the product.
A popular way to drive multiple lamps simultaneously is to have the lamps connected in parallel and powered by a single power supply module. However, lamps are known to require a larger starting current at a lower environment temperature. Therefore, if the power supply module still supplies a fixed alternating current when the lamps are exposed to a much lower environment temperature, some of the lamps may fail to start. Particularly, the starting voltage of the lamps and the starting voltage differences between the individual lamps will both increase as the environment temperature decrease, thus, preventing the lamps from starting up simultaneously. As a result, the overall applicability of the lamps will be decreased.
Accordingly, efforts still have to be made in the art to provide a dimming circuit that is able to conserve electric power and prolong the service life of the lamp.